For the preparation of precise impressions, such as those used in dentistry, and of working models, such as for dental technology, and of temporary denture parts, aziridine-containing substances are polymerized such as those described, for example, in U.S. Pat. Nos. 3,453,242 and 4,093,555. For this purpose the aziridine-containing compounds are commonly used together with fillers, coloring substances and further adjuvants.
Compounds suitable for the initiation of the polymerization reaction are the sulfonium salts known from U.S. Pat. No. 4,167,618 and having an electron-attracting group in the .beta. position to the central sulfur atom and a non-nucleophilic anion.
Furthermore, from EP-A No. 0 110 429 imidazoles present in a dissolved form are known as agents for delaying the polymerization of aziridine compounds.
It has been found that with the known systems the processing period of the initiated mixtures cannot be adequately adjusted for several purposes, especially for making very bulky working models, or at high external temperatures. Particularly in such cases it has been found that it is very difficult to combine a long processing period with a rather short setting time. For making a complete jaw impression, the processing period of the initiated mixture should be sufficient, for example, to place the material on an impression tray and into a syringe, eject the material around the prepared tooth stumps, and thereafter to introduce the filled impression tray into the patient's mouth. Only after this moment should the polymerization commence to take place as rapidly as possible in order that the impression can be removed after a short time without any dimensional change, with the time required for this operation still being acceptable for both the dentist and the patient. The situation is similar in the case of intraoral preparations of temporary denture parts or the preparation of jaw models by dental technicians.
It is thus the object of the present invention to provide compounds which are particularly effective in delaying the polymerization reaction of the aziridine compounds initiated by sulfonium salts without substantially prolonging the setting time.
It has been found that ionogenic compounds soluble or dispersible in aziridine compounds prolong the processing period of aziridine compounds blended with sulfonium salt initiators without substantially influencing the setting time, provided said ionogenic compounds contain anions which are more nucleophilic than the anions present in the sulfonium salts employed.
The subject matter of the present invention is thus a preparation for dental purposes containing three spatially separate components, namely,
(a) at least one aziridine compound, PA1 (b) at least one sulfonium salt initiator for (a), and PA1 (c) at least one ionogenic compound soluble or dispersible in (a) and having an anion that is more nucleophilic than the anion of (b). PA1 (a) at least one aziridine compound, PA1 (b) at least one sulfonium salt initiator for (a), and PA1 (c) at least one ionogenic compound soluble or dispersible in (a) and having an anion that is more nucleophilic than the anion of (b).
Moreover, the subject matter of the present invention is the use of an ionogenic compound soluble or dispersible in aziridine compounds for delaying the polymerization of aziridine compounds initiated by a sulfonium salt, said ionogenic compound containing an anion that is more nucleophilic than the anion present in the sulfonium salt employed.
Furthermore, the subject matter of the present invention is directed to a process for preparing dental impression compositions ready for use, which are characterized by the homogenously blending of
In this context soluble and dispersible means that the compound (c) is soluble in (a), or can be dissolved or dispersed in (a) by conventional measures, e.g., by the addition of solubilizing agents.
The classification of the anions as to their nucleophilic nature is made, for example, in the manner described by E. S. Gould in Mechanismus and Struktur in der organischen Chemie published by Verlag Chemie 1962, page 248 et seq. and 307 et seq., or by C. G. Swain, et al., in J. Am.Chem.Soc., 75, page 141 (1953) and A. B. Ash, et al. in J.Org.Chem, 34, page 4071 (1969).
The aziridine compounds (a) employed may be the initially mentioned compounds of U.S. Pat. Nos. 3,453,242 and 4,093,555, which compounds are incorporated herein by references. Examples of such compounds include, e.g., polyethers with terminal aziridino groups and bisphenol-A derivatives with terminal aziridino groups.
Suitable sulfonium salt initiators (b) are described in U.S. Pat. No. 4,167,618 and incorporated herein by reference, among which the sulfonium salts containing nitrile or ester groups positioned .beta. to the S atom are preferred. Especially preferred initiators are sulfonium salts with fluroborate anions which exhibit high activity as well as excellent stability. The amount of sulfonium salts employed normally ranges from 1 to 8% by weight, based on the weight of the aziridine compounds, such as those described in U.S. Pat. No. 4,093,555 and from 2 to 20% in other aziridine compounds, by weight, based on the weight of the aziridine compounds.
The ionogenic compounds (c) are employed in quantities of 0.1 to 15% by weight, based on the weight of the aziridine compounds. Quantities of from 1 to 10% by weight are especially preferred.
The ionogenic compound (c) is present either as such, primarily if it is present in liquid form, or in dissolved or dispersed form, especially if the melting point is above room temperature. Suitable solvents or dispersants are substances employed in the plastics processing industry as plasticizers, e.g., phthalates and citrates.
The ionogenic compound or the solution or dispersion thereof may be present with fillers or pigments and optionally with additional adjuvants in pasty form. This is advantageous if also the components (a) and (b) are present in a pasty consistency, because in that case the components (a) to (c) can be metered by the length of the paste extrudate (volume) and blended.
The preparation of the ionogenic compounds used according to the present invention is known. A number of substances are available on the market.
By the use of component (c), the polymerization of the aziridine compound (a) initiated by the sulfonium salt (b) can be substantially delayed. By varying the amount of (c), the setting time of (a) can be varied widely.
A further advantage of the preparation of the present invention is offered by the possibility of using highly reactive and highly stable sulfonium salt initiators (b). They preferably have a nitrile substitutent positioned .beta. to the central sulfur atom, and a fluoroborate anion.
With the use of sulfonium slats (b) containing a fluoroborate anion, suitable ionogenic compounds(c) are selected from compounds containing anions that are more nucleophilic than the fluoroborate anion. Suitable anions are, for example, the F, I, Br, Cl, sulfonate, sulfate, alyylsulfate, arylsulfate, and carboxylate anions. Especially preferred anions are sulfonate, alkylsulfate, and carboxylate anions, especially benzenesulfonate, xylenesulfonate, p-toluene-sulfonate, ethosulfate, methosulfate, and laurinate anions, as well as fluoride, bromide, chloride and iodide.
The cation of compound (c) normally performs the function of rendering the ionogenic compound soluble in the aziridine compounds. Cations suited for this purpose are, for example, quaternary ammonium and phosphonium, or tertiary sulfonium cations. Especially suitable are quaternary ammonium cations, for example, tetrabutylammonium, ethyl trioctylammonium, butyl trioctylammonium, ethyl triisooctylammonium or ethyltrihexylammonium cations.
Examples for suitable ionogenic compounds (c) in combination with fluoroborate sulfonium salts are: trioctyl ethylammonium xylene sulfonate, triisooctyl methylammonium tosylate, trioctyl butylammonium tosylate, trioctyl ethylammonium benzensulfonate, trioctyl ethylammonium ethosulfate, trioctyl ethylammonium laurylsulfonate, triisooctylammonium ethosulfate, tributyl ethylphosphonium tosylate, triisooctyl ethylammonium trifluoroacetate, dodecyl benzenesulfonic acid potassium salt, tetrabutylammonium laurinate, trihexyl ethylammonium tosylate, trihexyl ethylammonium benzenesulfonate, tetrabutylammonium iodide, tetrabutylammonium bromide, tetrabutylammonium tosylate, tetrabutylammonium trifluoroacetate, triisooctyl ethylammonium-p-tosylate, tetrabutyl phosphonium chloride, phenylethyl disbutyl ethylammonium chloride, triisooctyl methylammonium p-toluenesulfonate, .beta.-phenylethyl disbutyl methylammonium iodide, methyl trioctylammonium chloride, trioctyl butylammonium bromide.
In case sulfonium salts (b) with p-toluenesulfonate, alkylsulfate or benzenesulfonate anions are employed, suitable retardant substances (c) are, for example, iodide, bromide, chloride and compounds containing similar anions.